The present invention relates generally to a manner by which to reduce current consumption during operation of a communication device, such as a cellular mobile station powered by a portable power supply. More particularly, the present invention relates to apparatus, and an associated method, by which to operate portions of the cellular mobile station, or other communication device, at a desired power level, but at reduced current consumption levels, thereby to reduce power consumption of the device and increase longevity of the portable power supply thereof.
Advancements in communication technologies have permitted the implementation, and popular usage, of multi-user radio communication systems. A cellular communication system is exemplary of such a radio communication system. Information signals generated during operation of a radio communication system are transmitted upon radio communication channels.
To convert the information signal into a form to permit its communication upon a communication channel defined in a radio communication system, a transmitting station modulates the information signal upon a carrier wave of a carrier frequency within the range of frequencies which defines, at least in part, the communication channel. Thereby, a baseband-level signal of which the information signal is formed is converted into a radio frequency signal corresponding to the frequency of the communication channel upon which the resultant, communication signal is to be transmitted to a receiving station.
A transmitter of which the transmitting station is formed includes one or more up-mixing stages at which the baseband, information signal is up-converted in frequency to be of the selected radio frequency. The mixing stages include mixer circuits coupled to receive the information signal and an up-mixing signal with which the information signal is to be multiplied or otherwise combined to form an up-converted signal. When multiple mixing stages are utilized, an IF (intermediate frequency) signal is formed at a first, or first series, of the mixer stages. A radio frequency signal is formed at the final mixing stage.
The receiving station which receives a radio-frequency, communication signal transmitted thereto upon the radio communication channel must, analogously, convert the radio frequency signal to a baseband level. One or more down-conversion stages is utilized to down-convert the radio frequency signal to a baseband-level. Typically, an antenna transducer converts the radio-frequency communication signal transmitted upon the communication channel into electrical form. When initially converted into electrical form, the signal is of small amplitude. Amplifier elements forming a portion of the receiver of the receiving station amplify the received signal. Because of the amplification of the received signal, during down-conversion, such as at an IF stage of the receiver, the elements of the receiver must exhibit highly linear characteristics to ensure proper operation of the receiver.
A mobile station is used by a subscriber to a cellular communication system and is used to communicate therethrough. A mobile station is a radio transceiver having a transmitter portion and a receiver portion, together housed in a housing permitting carriage by the subscriber. A portable power supply is typically attached to, or contained within, the housing of the mobile station. Radio communication with network infrastructure of the cellular communication system is provided by way of the mobile station without need for a wireline connection between the mobile station and the network infrastructure and without the need for connection of the mobile station to an external power supply.
However, because the mobile station is powered by a portable power supply, the time period during which the mobile station is operable is limited by the storage capacity of the portable power supply. When energy stored at the portable power supply is depleted, continued operation of the mobile station is not permitted without replacement, or recharging, of the portable power supply.
As the amount of energy required to power the mobile station is determinative of the operational period during which the mobile station can be utilized, any manner by which the level of power consumption required to operate the mobile station can be reduced would increase the time period during which the mobile station can be powered by the portable power supply.
If a manner could be provided by which to reduce the power consumption requirements of the mobile station, increased longevity of a portable power supply used to power the mobile station would be permitted.
It is in light of this background information related to portable communication devices that the significant improvements of the present invention have evolved.
The present invention, accordingly, advantageously provides a manner by which to reduce current consumption during operation of a cellular mobile station, or other communication device. Through operation of an embodiment of the present invention, longevity of a portable power supply used to power the communication device is increased as a result of the reduced current consumption, and corresponding power consumption, requirements of the circuitry of the communication device. By increasing the amount of time by which the portable power supply is able to power the communication device prior to replacement, or recharging, thereof, improved convenience of use by a user of the communication device is permitted.
In one aspect of the present invention, a manner is provided by which to reduce the level of current required to operate the transmit portion of the communication device. The transmit portion, in one implementation, includes a power amplifier operable to amplify a transmit signal to permit transmission of the transmit signal to the network infrastructure of the communication system. Such a power amplifier is biased by a bias current. Generally, the power amplifier is constructed in a manner such that minimum performance requirements required thereof are met at a maximum output power level of the transmit signal, once amplified by the power amplifier. At the maximum output power level, the power level is self-biased. That is to say, the power level of the transmit signal applied to the power amplifier, together with the construction of the amplifier, sets the quiescent operating point thereof. When the power level of the transmit signal applied to the power amplifier is reduced beneath a threshold level, the power amplifier no longer remains self-biased. Instead, the power amplifier becomes biased by the biasing current applied thereto, and the gain of the power amplifier, and the transmit signal amplified thereat, is controlled by the level of the biasing current. Advantageous use of the operation of the power amplifier is made to control current consumption of the power amplifier as the biasing current applied to the power amplifier can be reduced without affecting the output power level of the transmit signal, once amplified, when the amplifier is self-biased to be operable in a self-biased mode.
In another aspect of the present invention, the transmit portion of the communication device further includes a power amplifier driver operable at a high, fixed current level. The driver includes a feedback pack which provides linearity performance of a desired level to the power amplifier driver. The gain of the amplifier driver is fixed, and the linearity of the amplifier driver is tied to a biasing current applied thereto. As the output power level of a signal amplified by the amplifier driver decreases, the bias current can be reduced, also to reduce current consumption of the transmit portion of the communication device.
In another aspect of the present invention, the transmit portion of the communication device also includes a RF (radio frequency) mixer. The RF mixer exhibits a characteristic gain in linearity. The gain in linearity of the RF mixer are of levels responsive to a bias current applied to the RF mixer. By appropriate alteration of the level of the biasing current applied to the RF mixer, the current consumption of the mixer is alterable and the gain of the RF mixer is correspondingly alterable. Lowering the level of the biasing current applied to the RF mixer reduces the current consumption, and corresponding power consumption, of the mixer.
In one implementation, an embodiment of the present invention is operable in the transmit portion of a cellular mobile station. The transmit portion includes an RF mixer, a power amplifier driver, and a power amplifier. At high power levels, such elements are biased for maximum linearity. As the output power level required of an output signal generated by the transmit portion is reduced, the gain of the RF mixer is reduced. Correspondingly, the biasing current applied to the power amplifier driver is reduced as the output power level is reduced. Eventually, the power amplifier is no longer self-biased, and the gain of the power amplifier becomes tied to the biasing current applied thereto.
In another aspect of the present invention, a manner is provided to selectably reduce the current consumption of the receive portion of a communication device. By reducing the current consumption of the receive portion of the communication device, the power consumption of the device correspondingly is reduced. When the communication device is powered by a portable power supply, reduction in the power consumption of the device increases the longevity of the portable power supply as the dissipation of the stored energy of the portable power supply is also reduced.
In one implementation, the receive portion of the communication device includes a Low Noise Amplifier (LNA). The low noise amplifier is selectably biased by a biasing current. Determinations are made of a signal-to-noise ratio of a receive signal received at the receive portion of the communication device. If the ratio is greater than a selected threshold, the low noise amplifier need not be utilized to amplify the receive signal. And, the biasing current is not applied to the low noise amplifier. If, conversely, the signal-to-noise ratio is less than the threshold, the low noise amplifier is biased with the bias current, thereby to amplify the receive signal. Through operation of such an embodiment of the present invention, current consumption of the receive portion of the communication device is selectably reduced when the signal-to-noise ratio of the receive signal is greater than the selected threshold.
In these and other aspects, therefore, apparatus, and an associated method, is provided for a radio device operable in a radio communication system to communicate radio frequency communication signals. The radio device is operated at selected radio characteristics. A first amplifier element is coupled to receive a first radio frequency signal. The first amplifier is biased by a first-bias current signal of a first selectable biasing level. The first amplifier element generates a first amplified radio frequency signal exhibiting a first level of linearity wherein the first level of linearity is responsive to the first-bias current signal. A second amplifier element is coupled to receive indications of the first amplified radio frequency signal generated by the first amplifier element. The second amplifier element is selectably operable in a large signal mode and in a small signal mode. The second amplifier element is operated in the large signal mode when the indications of the first amplified radio frequency signal applied thereto is at least as great as a threshold value such that, when operated in the large signal mode, the second amplifier element becomes self-biased at fixed gain level.
A more complete appreciation of the present invention and the scope thereof can be obtained from the accompanying drawings which are briefly summarized below, the following detailed description of the presently-preferred embodiments of the present invention, and the appended claims.